Creating fragmentation

Hi,

I'm tring to configure a WAN simulator under Linux. I'm using Netem
for latency, reorder, drop..
But I don't know how to create fragment.
For example, I'd like to simulate something like that :
A <---> {ethernet (mtu 1500)} <---> (X.25 (mtu 576)} <---> {ethernet
(mtu 1500)} <---> B

So my packets coming from A are fragmented.

Things I've tried with my box with 2 ethernet cards :
- changing mtu from eth0, eth1 and wan (bridge)
- using the set-mss from iptables : iptables -t mangle -A POSTROUTING -
p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 576

But that doesn't work.

Have you any idea to do that ?

Thanks and sorry for my english